1. Field of the Invention
The present invention relates to an aqueous ink composition for a ball-point pen.
2. Description of the Related Art
Conventionally, an aqueous ink for a ball-point pen has been disclosed in Japanese Patent Laid-Open No. 59-74175 or Japanese Patent Laid-Open No. 59-138281.
The aqueous ink disclosed in Japanese Patent Laid-Open No. 59-74175 contains xanthane gum of between 0.20 to 0.45 wt. %, and the aqueous ink disclosed in Japanese Patent Laid-Open No. 59-138281 contains xanthane gum of between 0.20 to 0.45 wt. % and a permeable drying agent of between 0.5 to 10.0 wt. %, for providing pseudo plasticoviscosity.
However, since xanthane gum is an ionic polysaccharide, when a large amount of xanthane gum is used, it reacts with an ionic component in the ink, preservation stability is impaired, and phenomena such as ink shortage, dripping, or dripping-down occur at an ordinary (e.g., operating) temperature for a half year to one year, resulting in writing failure. To solve these problems, Japanese Patent Laid-Open No. 6-256700, provides aqueous ink for a ball-point pen containing xanthane gum of 0.2 wt. % or less and a non-ionic polysaccharide of 0.01 to 0.5 wt. %, thereby improving stability over time.
When xanthane gum and non-ionic polysaccharide are mixed together, ink preservation stability is improved. However, because of non-ionic properties of polysaccharide, when the non-ionic polysaccharide is added, lengthy stirring must be performed to disperse the non-ionic polysaccharide. In addition, even after the ink has been prepared, when microscopic observation is performed to confirm the dispersion state of a pigment, there have been observed blocks of any components failing to disperse. This problem leads to writing failures.